One who flashes their brights at other cars for no reason.
Note- there are many reasons for flashing one's brights. One of the most common reasons for flashing your brights at an oncoming car (often done twice in quick succession) is to warn the driver of a police car (popo)nearby so that the driver does not get caught speeding.

"Turns out that dude wasn't a flashole; there's a speed trap up here."